President Juan Manuel Santos said the National Liberation Army, known by its Spanish initials ELN, must first free a former congressman it has held captive for six months.

The delay may have been a simple matter of logistics. Chief government negotiator Juan Camilo Restrepo said in a statement that the International Red Cross had informed authorities that operations have begun to receive the ex-congressmen, Odin Sánchez.

A Red Cross spokeswoman said the organization had no immediate comment on the matter.

The talks' ceremonial opening had been planned for Thursday in Quito, but Santos previously said they would not commence until the ELN freed Sánchez.

The planned talks come amid deep uncertainty over the narrow electoral defeat in an Oct. 2 referendum of the government's peace pact with Colombia's main rebel group, the Revolutionary Armed Forces of Colombia. Negotiators from both sides are in Cuba trying to salvage that pact, which was reached after four years of thorny negotiations.

The ELN is far smaller than the FARC and was founded in the same year, 1964. Inspired by the Cuban revolution, it is ideologically more doctrinaire and recalcitrant than the FARC, which grew out of peasant self-defense forces.

The ELN has funded itself through kidnapping and extortion and is most active in the oil-producing northeastern state of Arauca bordering Venezuela.

It has fewer than 2,000 fighters, making it less than one-third the size of the FARC.

Odin Sánchez swapped himself in April for his brother Patrocinio, former governor of the poor Pacific state of Choco, after Patrociono fell ill. He had been held since 2013.